Check team member instead of session for team admin role when updating/deleting channels (#3007)

i18n/en.json

@@ -3379,6 +3379,10 @@
     "id": "store.sql_team.get_by_name.app_error",
     "translation": "We couldn't find the existing team"
   },
+  {
+    "id": "store.sql_team.get_member.app_error",
+    "translation": "We couldn't get the team member"
+  },
   {
     "id": "store.sql_team.get_members.app_error",
     "translation": "We couldn't get the team members"